This invention relates in general to solenoid valves utilized in anti-lock brake systems and in particular to measurement of the movement of an armature within a solenoid valve.
An anti-lock brake system (ABS) is often included as standard equipment on new vehicles. When actuated, the ABS is operative to control the operation of some or all of the vehicle wheel brakes. A typical ABS includes a plurality of normally open and normally closed solenoid valves which are mounted within a control valve body and connected to the vehicle hydraulic brake system. Usually, a separate hydraulic source, such as a motor driven pump, is included in the ABS for reapplying hydraulic pressure to the controlled wheel brakes during an ABS braking cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body.
An ABS further includes an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, a plurality of solenoid coils associated with the solenoid valves and wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The control module is typically mounted upon the control valve body to form a compact unit which is often referred to as an ABS electro-hydraulic control unit.
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors. The microprocessor monitors the wheel speed signals for a potential wheel lock-up condition. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor and selectively operate the solenoid valves in the control unit to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.
As described above, an ABS typically includes a plurality of solenoid valves for controlling the flow of hydraulic fluid to the vehicle wheel brakes. Referring now to the drawings, there is shown generally at 10 a typical cartridge for a normally closed solenoid valve. In an ABS, such normally closed valves are typically referred to as xe2x80x9cdumpxe2x80x9d valves. The valve cartridge 10 includes a generally cylindrical valve body 11. An inlet port, which includes a stepped bore 12, extends axially through the valve body 11. The upper end of the stepped bore 12 is formed into a valve seat 13. A pair of outlet ports 14 are also formed in the valve body 11.
A tubular valve sleeve 15 extends axially from the top of the valve body 11. An axially slidable armature 16 is disposed within the valve sleeve 15. A valve ball 17 is mounted upon the lower end of the armature 16. The valve ball 17 co-operates with the valve seat 13 to control the flow of fluid through the valve cartridge 10. A cylindrical core 18 is secured in the upper end of the valve sleeve 15. A return spring 19 is disposed between the lower end of the core 18 and the upper end of the armature 16. The return spring 19 urges the armature 16 in a downward direction in FIG. 1 to maintain the valve cartridge 10 in a normally closed position. As shown in FIG. 1, when the cartridge 10 is in its normally closed position, a small working air gap, which is labeled GA, exists between the lower end of the core 18 and the upper end of the armature 16.
A dump valve also includes an annular flux ring and a solenoid coil (not shown) which slidingly extend axially over the valve sleeve 15 and core 18. The solenoid coil typically includes insulated magnet wire wound upon a plastic bobbin. A metal cup-shaped flux casing (not shown) encloses the coil and flux ring and is secured to the flux ring by a conventional operation, such as crimping to form a coil assembly. The flux casing and flux ring provide a return path for the magnetic flux when the solenoid valve is actuated. Typically, the coil assembly is attached to a Printed Circuit Board in the ABS control module and is removable from the valve cartridge 10 when the control module is removed for maintenance. When the coil assembly is removed, valve sleeve 15 maintains a sealed hydraulic brake circuit.
During operation, an electric current is passed through the solenoid coil. The resulting magnetic field causes the armature 16 to move in an axial upward direction within the valve sleeve 15 to compress the return spring 19. As the armature moves, the working air gap GA is closed and the valve ball 17 moves away from the valve seat 13 to open the solenoid valve. Upon the interruption of the electric current, the magnetic field collapses and the return spring 19 pushes the armature 16 in a downward axial direction to reset the valve ball 17 upon the valve seat 13 and thereby close the solenoid valve.
As indicated above, an ABS also includes normally open, or isolation, solenoid valves which have a structure similar to the dump valve described above. A cartridge for a typical isolation valve is illustrated in FIG. 7, where the working air gap GA exists between the lower end of the armature 16 and the upper end of the valve body 11.
This invention relates to measurement of the movement of an armature within a go solenoid valve.
As explained above, solenoid valves are important components in anti-lock brake systems. Therefore, it is desirable that such valves are properly assembled. For example, a manufacturer needs to confirm that a return spring has been included within each of the valves. Typically, the valve sleeve is press fit onto the valve body and secured with a laser weld. The axial position of the valve sleeve upon the valve body controls the working air gap between the valve armature and the valve core in a dump valve or the between the valve armature and valve body in an isolation valve. A typical working air gap has a tolerance of 0.004 inches. The size of the working air gap is especially critical in proportional solenoid valves.
It is known to test an assembled solenoid valve by removing the valve from its pallet and turning the valve over to expose a valve port formed through the valve seat. Such ports have a typical diameter of 0.013 inches. A slender test probe is inserted through the valve port and into contact with the valve ball mounted in the end of the valve armature. The test probe is connected to a Linear Variable Differential Transformer (LVDT). The solenoid coil for the valve is energized to axially displace the armature and test probe. The movement of the armature and the test probe, which is a function of the working air gap of the valve, is measured by the LVDT. The coil is then de-energized and the armature movement again measured by the LVDT. The test procedure confirms that the working air gap has the correct size and that a return spring has been included in the valve; however, the test is very time consuming and requires accurate placement of a delicate mechanical component. Accordingly, it would be desirable to provide a simpler method for measuring armature travel within a solenoid valve cartridge to verify correct assembly of the cartridge.
The present invention contemplates an apparatus for testing a solenoid valve cartridge which includes a coil adapted to be placed over the valve cartridge and a circuit for supplying an electric current to the coil. The circuit co-operates with the coil to form a window comparitor. The window comparitor switches the voltage applied to the coil on and off, with the voltage on time being a function of the inductance of the coil. The coil inductance is proportional to the size of the working air gap in the solenoid valve cartridge. Accordingly, the on time for the coil voltage is a function of the size of the working air gap of the solenoid valve cartridge.
The apparatus further includes a mechanism for positioning the coil over the solenoid valve cartridge before the current is supplied to the coil. The mechanism also removes the coil from the solenoid valve cartridge after the test is completed. The apparatus also can include a data logging device coupled to the circuit for recording the results of the test. The apparatus can additionally include a control unit coupled to the mechanism for positioning the coil over the solenoid valve cartridge. The control unit is also coupled to the circuit and is operative to actuate both the positioning mechanism and activate the circuit.
The invention further includes a method for testing a solenoid valve cartridge which includes providing a test fixture having a coil. The test fixture is placed over the solenoid valve cartridge being tested. The test fixture coil is energized and the duration of the on time for the voltage applied to the coil is observed. The duration of the voltage on time is then correlated with the size of the working air gap in the valve cartridge.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.